Theme: Tap water quality/Lead Testing
Grades: 9-12 Chemistry/Physical Science
Urban students are seldom interested in anything that does not effect them directly. They can avoid the water in lakes and streams, however, they cannot avoid water which they consume. Water quality in Milwaukee is always an issue (remember cryptosporidium?). Once students perceive the need to investigate further, after exposure to information provided by teacher demonstration and media supported articles, they will test their own water samples and report their findings.
Description of School:
John Marshall International Baccalaureate High School is an urban public high school with 1500 students of diverse ethnic and socioeconomic backgrounds. The majority of the students are inner city minority youth. Marshall is culmination of 85 percent African American, 7 percent Caucasian, 3 percent Hispanic, and 5 percent Asian individuals. John Marshall High School reflects the diversity of its learners by offering a comprehensive program that includes a School to Work initiative, a broadcasting and technology specialty program, and the recently attained International Baccalaureate program for the college bound.
Part A: The Diversion/Demonstration
The beginning of this unit starts in the classroom. At the beginning of class students are usually talking amongst themselves and need a diversion to direct their attention.
Ms. Wittig draws their attention by asking if anyone, and how many, would like something to drink. She then tells the students their order is coming right up and brings out pitchers of drinking water; all cold and delicious. She must also pour herself a glass and only drink half in their presence.(Make sure that the teacher's glass is a clear glass so that students can see the contents.) The remainder of the glass is to be used in the second part B. The students receive their refreshing drinks and are enjoying themselves when Ms.Wittig asks that anyone who wants seconds can raise his/her hand.
Part B: Activating Prior Knowledge
Ms.Wittig then brings out a pitcher of foul looking water that was hidden under the counter. (The water simply has sterilized sand floating in it which the teacher stirred up before it was brought to the surface.) She then encourages the students to have their second glass of water from the dirty pitcher. Students will obviously make noises of disgust; one might even hear a small chorus of, "Are you nuts?". The teacher then asks, "Why did you change your minds"? Students might reply, "That water looks nasty"! Ms. Wittig might then probes the class by asking, "What does the way water looks have to do with its quality"? A student might reply, "Water that we drink out of the faucet doesn't look like that; its clear". "Oh," Ms.Wittig replies, "I can fix that". Next a filter system created from an old two liter soda bottle is brought out. The teacher pours the water through the filter and captures the remaining effluent on the other end. (This may take a little time, so move on to part C)
Part C: Presenting a Discrepant Event
Ms.Wittig continues the conversation, "While we are waiting for the water to filter, let me ask you about this pitcher of water". Another pitcher of water is brought out from under the counter that appears to be the same as the water they drank; clear and cold. (This pitcher of water has been rigged with an impurity of dilute sodium hydroxide.) Ms.Wittig asks the students:
- Is this what water should look like?
- Well students, besides drinking the water myself how could this water be tested to make sure it is safe?
- What are the chemical and physical properties of water that we know? The teacher may need to lead the students to the characteristic properties.
Responses from the class might include:
- It is clear and colorless.
- It boils at 100 degrees Celsius.
- Water freezes at zero degrees Celsius.
At this point Ms.Wittig directs the discussion:
- What experiment can we devise to check for these physical properties?
- What data should be kept track of.
- How will the data be organized and presented.
- What types of graphs could you use.
Students may offer the following:
- Heat ice water until it boils and keep track of the temperature every minute.
- Make a line graph to see the rise in temperature per minute and then look for places where the temperature reaches plateaus.
"Well, we could run that test", says Ms.Wittig, "but let me show you another test we haven't done yet". "Who has heard the term pH and can tell me what it means", she asks. If this topic hasn't been covered yet no one will be able to offer any answers. Ms. Wittig might then ask the following:
- What makes water different from lemon juice?
- What make water different from liquid drain cleaner?
Students might reply:
- Drain cleaners eats away at garbage that plugs up your pipes when water can't get through.
- Lemons taste sour.
- Lemon juice makes your skin itch.
- Drain cleaners can burn your hands.
- Drain cleaners are poison.
After useful responses are offered Ms.Wittig explains what acids and bases and indicators are and then follows up with a demonstration. Three tall cylinders of clear liquid are placed on the counter; one labeled acid, one labeled water, and one labeled base. Into each cylinder 5 drops of universal indicator is placed; the contents are stirred with a glass rod and the students can see the colors created. Ms.Wittig asks a student to identify the label on each tube and describe the color present. Responses from the students should be:
- The acid tube is red/orange.
- The water tube is green.
- The base tube is violet.
"This is very similar to the rainbow isn't it", Ms.Wittig asks. "What color is in the middle of the rainbow", she asks. A student might reply, "Green is the color in the middle". "Good", Ms.Wittig responds, "now let's connect those thoughts to compare the rainbow to the colors of water in the tubes". "Tanesha, why would the color of water be green when the indicator is in it", Ms.Wittig asks. Tanesha guesses, "Because water is not an acid or a base". "That's it", responds the teacher, "and solutions that are neither acid nor base are considered to be neutral".
Ms. Wittig then holds up the third pitcher of water and asks the students again if they would drink water from this pitcher, yes or no, and why or why not. Once enough students are solicited she moves on to prove to the students that the water is not drinkable by using the universal indicator; the solution turns violet.
Part D: Tying Up Loose Ends
Ms.Wittig then summarize what has been learned so far and makes the following points:
- You drank the glass of water that was given to you and enjoyed it.
- You didn't want water from the second pitcher because it looked unappealing to you.
- I poured the water from the second pitcher into the filter I had and said that I could "fix" the problem.
- We discussed the physical properties of water and you told me how you would test it.
- We discussed a new test for identifying a property of water; pH.
- We tested the water from the third pitcher and found that it was not pure water because the indicator did not turn green.
At this point Ms.Wittig places her glass half full of water on the table next to the glass of the water captured by the filter system. The teacher ask what changes in the water do the students notice and if they think it is drinkable. Responses might be:
- The water looks clear.
- I still don't know it it is clean water.
- I still wouldn't drink it.
- It might be an acid or a base like the other pitcher of water.
The teacher then puts a few drops of universal indicator in the effluent and the water turns green. The teacher then explains the set up.
The teacher wraps up the discussion with, "Here in this city we are fortunate, our water is filtered by the water department for the city. There are standards that must be met before the water can pass through the pipes to us. Recently, though, in Milwaukee many people got sick from drinking city water because of an organism called cryptosporidium. Remember, the people could not tell that the organism was in the water by site, taste, or smell; but, boy they sure felt the difference. Since then steps have been taken to screen more carefully for cryptosporidium. There is, however, another danger that is rarely talked about, but truly exists in this city; exposure to lead in drinking water. I would like you to read the following article and I would like you to come up with points to discuss tomorrow".
Summarizing the Article
After reading the article on lead exposure, the class will be polled as to what points were made by the article. Students may offer the following points:
- America's municipal drinking water is one of the safest in the world.
- Standards are in place that help ensure that the water is of the best quality.
- Chlorination is used to kill bacteria.
- Chlorination cannot take care of everything that is in the water.
- Some things that are not good for people; like lead, may still be in the water, but are not required to be tested according to the Clean Water Act of 1972.
After these points are made Ms.Wittig asks the students, "What would you like to know about your drinking water"? A student is assigned to keep track of the questions on a transparency for later use. Some of the responses might be the following:
- Where is our drinking water cleaned?
- How is our drinking water cleaned?
- Where does the water enter the plant?
- What kinds of tests are run to make sure that the water is drinkable?
- Who runs the tests on the water before it is released?
- What type of training/schooling do the municipal workers have?
- How can I tell if I have something in my water that shouldn't be there?
Students will be guided to concentrate on lead. The teacher might say, "Most bacterial forms are taken care of the article says, but remember, lead is one of those things that isn't tested for by the municipal water department". "What would you add to the list to find out about lead", asks the teacher. Students might respond:
- How does lead get into the water?
- How can lead be prevented from getting into the water?
- How can you tell the amount of lead in the water?
- How much lead would it take to make you sick?
- What does lead do to people?
Any other valid questions may be added to this list as necessary. The teacher then informs the students that he/she knows of a test to measure the amount of lead in water and asks if the students would like to test their water from home to see if it contains lead. The response is a favorable one, and so, the teacher moves forward to discuss the project.
The students are responsible for designing the sampling process of water. The conditions under which the water is drawn must be the same for each student at home. The instructions for water sampling might include the following:
- The time of day the water is tapped.
- Whether water from the cold tap or the hot tap will be selected.
- How much water should be brought in.
- What type of container will the samples be stored in.
- How will the samples be stored until the testing is done.
- When will the testing be done.
- What would be important things to keep in mind to make sure that the samples are not contaminated by other sources.
- What will be the control.
The teacher reminds the students that since water runs through pipes that they should take note as to the type of pipes they have in their home.
Ms. Wittig has reserved the computer lab for the class on Monday, Wednesday, and Friday for six weeks. Mr. Everson will diligently monitor to see that the equipment is up and running properly so that students can utilize the computers to their fullest capacity.
In the computer lab students will be seen researching articles that have been linked into the project. They may also contact experts as needed via e-mail. Since there are a number of questions asked within each role more than one student will be working on the questions. The work will be evenly distributed within the group and the students will be seen asking one another for help and sharing ideas. Ms. Wittig circulates around the room checking to see if students are on task and giving guidence. Other schools have similar programs and can be contacted via the internet. Information that is gained or shared will be posted to our school web site which can be updated on a regular basis.
In the classroom, students are investigating qualitative analysis, ion formation, and ion detection. Students are introduced to the lab procedure and allowed to practice on stock solution samples. Ms.Wittig makes sure that safety procedures are followed and interacts with each student to assess whether or not they are comfortable with the procedure. Students are instructed to tap their home sources and bring them in for sampling.
When enough of the class is comfortable with the laboratory procedures, Ms.Wittig will assign a competent student to an insecure one. The students will run their tests, collect their data, and clean their area. The data will be posted to the web page.
Using the daily assignment sheets, Ms.Wittig can keep track of where the students have been and see if they are on track. She will often write personal notes to help guide the student in the right direction and give positive feedback on a daily basis. The students will be using these daily assignments as part of their notes. Granted, a journal may work just as well for students, but Ms.Wittig knows that she must stay on top of her students.
In the sixth week of the project students will be presenting their information as an oral report at the town meeting. When the class has heard all of the information presented they must decide on which direction to go with the information. All of the tests will be done and the results posted.
If the concentration of lead in the drinking water at or above standard levels there are many options available. Students will want to share the information with their parents, as well as, what preventative measures they can take. Students will be encouraged to report their findings to the Department of Health and Human Services, or the Environmental Protection Agency. Or, students may come up with any other feasible plan to utilize the information. Ms.Wittig will be excited to hear what they choose to do.